Streamflow forecast changes with declining snowpack

The USDA’s Natural Resources Conservation Service has changed its streamflow predictions in the Flathead River basin for the rest of the year because high-elevation snowpack is melting earlier than normal.

On May 6, NRCS reported that snowpack levels through the end of April were down to 69 percent of average in the Flathead River basin and down to 42 percent in the Kootenai River basin. That’s a slight decrease from last month.

Forecasted streamflows for the two rivers have also dropped. The average streamflow through the end of July is expected to be 87 percent of average for the Flathead River and 80 percent for the Kootenai River.

Because of the low snowpack levels, actual streamflows through the end of the summer will be more variable and dependent on precipitation levels, NRCS hydrologist Lucas Zukiewicz said.

“(Snowpack) is going to come out a lot quicker than it normally would, so we’re going to be a lot more reliant on precipitation during the summer to keep water in the streams,” he said.

Low temperatures above 6,000 feet at the beginning of April helped maintain snowpack, but high-elevations snows began melting more quickly than usual last month. By mid-April, snow at all elevations had begun to make that transition, NRCS reported.

Compared with the rest of the state and most of the West, Northwest Montana has been in good shape this year, having benefited from heavy snowfall early in winter and additional snowfall in the high elevations during February and March.

But that trend started to turn around in April, Zukiewicz said, and the mountains got about half their normal precipitation for the month.

According to the National Weather Service in Missoula, Kalispell registered 0.35 inches of precipitation in April — well below the average of 1.24 inches.

“We did see the persistence of this warm, dry weather pattern that we’ve had,” Zukiewicz said. “It might have been one of the first months west of the Divide that you’ve been getting what most of the state has been getting. But people that live in that area are still fairly fortunate — those are some of the highest stream flows in the state.”

Elsewhere in Montana, this summer is shaping up to be an even drier one. The Missouri River’s forecasted streamflow is 47 percent of the average. The Yellowstone River is at 67 percent. Statewide, rivers and streams are forecast to run at 69 percent of average.